So who are you calling bird brain? Chatter of chickens proves they are brighter than we thought

Why did the chicken cross the road? To impress scientists with its grasp of "representational signalling", according to research published today that suggests that hens are not bird brains after all.

A brighter view of the common chicken emerges in the journal Biology Letters, in which Dr Chris Evans and his wife Linda reveal that the birds have a far more sophisticated communication system than traditionally thought.

Communication is ubiquitous in the animal world but scientists usually write off these signals as reflecting the emotional state of a creature, whether fearful, angry or amorous. Previously, it was thought that the ability to denote things in the world — for example, food, hawk, fox — was unique to humans.

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To investigate what the birds are capable of telling each other, the team played food calls to adult golden Sebright bantam hens, which were selected because of the similarities between their calls and those of the red jungle fowl (Gallus gallus) from which all hens have been domesticated.

Rather than simply celebrating the discovery of food, the equivalent of a "hooray", the scientists discovered that the high-pitched "tck, tck..." that the birds made actually means "here is some food" — marking out an example of representational signalling.

"Hens responding to food calls do so because these sounds encode information specifically about food," said Dr Evans.

Tests on 17 birds showed that the calls made fellow hens scratch around to look for feed, but only if they had not recently discovered food — that is, only when the signal provided new information.

Dr Evans said that monkeys and other primates were known to use specific calls when they discovered food but this was the first such demonstration for a nonprimate species.

The hens even have nuances for a given call, producing them at a higher rate if the food is highly preferred. "For example corn evokes calls that are clearly distinct from those given to their regular ration," Dr Evans said. "There is hence a strong parallel between the cognitive mechanism engaged by representational signals and the denotative function of words."

Sophisticated communication of this kind may be the product of common social factors "rather than an attribute of our own evolutionary lineage", he said. "To the extent that our attitudes toward animals are shaped by their perceived mental life, such findings should be thought-provoking."

The cleverness of chickens goes further than the 20 or more calls they can make, however. For instance they live in stable social groups and can recognise each other by their facial features.

Studies by other researchers have shown that the birds have the ability to understand that an object, when taken away and hidden, nevertheless continues to exist, a feat beyond the capacity of small children. They are also good at solving problems.

"As a trick at conferences I sometimes list these attributes without mentioning chickens," said Dr Evans. "People assume that I'm talking about monkeys."